Lab focus questions -- echinoderm/frog/chicken development lab

Question 1

echinoderm development:

what is the difference b/n an oocyte and an egg?

Answer 1

an oocyte becomes an egg when meiosis is complete

Question 2

echinoderm development:

what is the difference b/n an egg and a zygote?

Answer 2

an egg becomes a zygote when fertilization is complete (that is, when the haploid sperm and egg nuclei fuse to become 1 diploid nucleus)

Question 3

echinoderm development:

what indication is there that the sea urchin egg has an animal-vegetal polarity?

Answer 3

polar – 2 ends that are not identical
sea urchin eggs show polarity

top – animal hemisphere
bottom – vegetal hemisphere

structures that develop from animal hemisphere are different than structures that develop from vegetal hemisphere

difference probably based on differences in info stored in the cytoplasm of the animal and vegetal hemispheres

one easily observable indication of polarity in sea urchin eggs – nucleus is offset towards the animal pole

Question 4

echinoderm development:

what are the biochemical consequences of egg activation?

Answer 4

rates of RNA and protein synthesis increase dramatically

DNA is synthesized in anticipation of cell division

Question 5

echinoderm development:

what must happen to restore the diploid condition during fertilization?

Answer 5

the haploid egg and sperm nuclei must fuse to become the diploid zygote nucleus

Question 6

echinoderm development:

what is polyspermy?

Answer 6

polyspermy is the fertilization of an egg by more than 1 sperm cell

Question 7

echinoderm development:

what problem does polyspermy present?

Answer 7

w/ more than 2 sets of chromosomes (1 from sperm and 1 from egg nucleus) –> there can be abnormal development

Question 8

echinoderm development:

what minimizes chance for polyspermy?

Answer 8

2 basic mechanisms to prevent polyspermy –

a fast polyspermy block – electrical

a slower polyspermy block (lifting off of the fertilization membrane)

Question 9

echinoderm development:

what is meant by holoblastic cleavage?

Answer 9

holoblastic cleavage – vertical cleavage furrows completely cut thru the egg from animal to vegetal pole

Question 10

echinoderm development:

what is the sequence of division plane orientation in early holoblastic cleavage?

Answer 10

first 2 cleavages are vertical and perpendicular to each other

3rd cleavage is horizontal

Question 11

echinoderm development:

what constitutes the ectoderm, the endoderm, and the mesoderm of the sea urchin embryo?

Answer 11

ectoderm – outer cell layer of gastrula

endoderm – archenteron (primitive gut)

mesoderm – consists of:

• primary mesenchyme cells that migrate into the blastocoel from the basal plate of the blastula as gastrulation begins (which form the skeleton)
• secondary mesenchyme cells that migrate from the invaginating archenteron (which form muscle cells)

Question 12

development lab focus questions:

what are some indicators of animal-vegetal polarity in eggs?

Answer 12

sea urchins – nucleus is offset toward the animal pole

amphibians –

• nucleus is offset toward the animal pole
• more dense yolk in the vegetal hemisphere than in the animal hemisphere
• there is pigment on the surface of the animal hemisphere

chickens –

• nucleus is offset toward the animal pole
• there is very dense yolk in the vegetal hemisphere

Question 13

development lab focus questions:

what is the effect of yolk on early development?

Answer 13

yolk affects cleavage

amphibians – yolk retards cleavage as it proceeds toward the vegetal pole

2nd cleavage begins in the animal hemisphere before the first is complete in the vegetal half

3rd (horizontal) cleavage is closer to the animal than to the vegetal pole (perhaps where there is less resistance to the formation of a cleavage furrow) –> yields animal blastomeres that are smaller than the vegetal blastomeres

later cleavage is more rapid in the animal hemisphere than in the vegetal, so that animal hemisphere blastomeres continue to be smaller than vegetal blastomeres

chickens – there is a very large amount of yolk in eggs – so much that only a very small portion of the cell at the animal pole, the blastodisc, is free enough from yolk to have any cleavage occur in it at all

Question 14

development lab focus questions:

how does cleavage in echinoderms, amphibians, and birds compare?

Answer 14

echinoderms – cleavage is holoblastic

amphibians – cleavage is holoblastic, but slow at the vegetal pole

chickens – cleavage is restricted to the animal pole. Cleavage of the chick zygote is quite different from that in echinoderms and amphibians. The first several cleavages are vertical, and extend only a very short distance downward; horizontal cleavages eventually occur, which give rise to several layers of blastomeres the make up a disc of cells situated on top of the mass of yolk below

Question 15

development lab focus questions:

how does the formation of the blastula in echinoderms, amphibians, and birds compare?

Answer 15

echinoderms – the wall of the blastula is 1-cell thick all around; blastocoel forms so that it occupies the animal and vegetal hemispheres essentially equally

amphibians – floor of the blastocoel is considerably thicker than the roof of the blastocoel. the blastocoel forms essentially exclusively in the animal hemisphere of the blastula

birds – the blastocoel is a very narrow space underlying the blastodisc, sitting on an enormous amount of yolk

Question 16

frog/chicken development:

echinoderms develop from eggs that have ___ yolk

Answer 16

very little

Question 17

frog/chicken development:

amphibians develop from eggs that have ___ yolk

Answer 17

a moderate amount of

Question 18

frog/chicken development:

birds develop from eggs that have ___ yolk

Answer 18

huge amounts of yolk

Question 19

frog/chicken development:

amount of yolk in an egg influences considerably the way….

Answer 19

early development progresses, particularly w/ respect to cleavage patterns and to morphogenesis

Question 20

development lab focus questions:

how does gastrulation in echinoderms, amphibians, and birds compare?

Answer 20

echinoderm gastrulation – like the classic pushing the leaky tennis ball – an invagination from the vegetal pole into the blastocoel

amphibian gastrulation – an involution of cells just ventral to where the gray crescent was located in the zygote – this inward movement continues as cells of the animal hemisphere migrate down over the larger yolky cells of the vegetal hemisphere

bird gastrulation – 2 steps:
1) lower layer of blastodisc cells migrates away – form a layer of hypoblast cells below the epiblast (which the remaining cells fo the blastodisc are now known as)

2) as hypoblast expands, the epiblast cells migrate rearwards and medially to form the primitive streak, thru which streak cells migrate to form the mesoblast, a layer of cell b/n the epiblast and the hypoblast

Question 21

development lab focus questions:

what are some derivatives of ectoderm, mesoderm, and endoderm in amphibians and birds?

Answer 21

ectoderm – epidermis of the skin, hair, nails, lens, cornea, entire nervous system; lining of the nose and mouth

mesoderm – muscle, bone, cartilage, notochord, blood, kidneys, gonads

endoderm – lining of esophagus, stomach, intestine; lungs, liver, pancreas, thyroid, parathyroids, bladder lining

Question 22

what are indicator(s) of animal-vegetal polarity in eggs?

Answer 22

distribution of pigment in the egg

distribution of yolk in the egg

location of the nucleus in the egg

Question 23

how does cleavage differ b/n frog zygotes and chicken zygotes?

Answer 23

frogs – cleavage occurs throughout the cytoplasm of frog zygotes, both in animal and vegetal hemispheres

chickens – cleavage is restricted to the animal hemisphere

the large amount of yolk in the vegetal hemisphere of a chicken egg prevents cleavage there, so cleavage is restricted to the animal pole

Question 24

which of the following do the blastulas of the sea urchin, frog, and chicken embryos hold in common?

Answer 24

presence of a cavity called the blastocoel

the blastocoel is a distinctive feature of the blastula

Question 25

which of the following is/are true of polyspermy?

Answer 25

polyspermy may occur if the fertilization membrane fails to form

fertilization membranes lifts off surface of egg after first sperm makes contact. But while forming, electrical block protects just-fertilized egg

Question 26

what types of zygotes show holoblastic cleavage?

what types of zygotes don’t show holoblastic cleavage?

Answer 26

yes:

mammal zygotes
amphibian zygotes
echinoderm zygotes

no:
chicken zygotes (only very small portion of cell at animal pole -- blastodisc -- is free enough from yolk to have any cleavage occur in it at all)

Question 27

cleavage in early mammalian embryos is most like the cleavage in which of the following?

Answer 27

early echinoderm embryos

echinoderm eggs have little yolk in them, like mammalian eggs. The amount of yolk in the egg can determine cleavage patterns.

Question 28

which of the following is true of the first three cleavages in echinoderm development?

Answer 28

the first 2 cleavages are vertical, the 3rd is horizontal

Question 29

what occurs during sea urchin development?

Answer 29

formation of mouth from archenteron

formation of anus from blastopore

archenteron developing from an inward buckling of the vegetal plate

formation of a fertilization membrane